The present invention relates to electrical power distribution systems. It has particular but not sole application to automotive starting, lighting and ignition (SLI) systems, and power distribution thereto from automotive batteries, hereinafter referred to as SLI batteries.
The conventional automotive SLI Battery consists generally of six 2.2 volt Lead Acid cells connected in series. It is a primary function of the automotive battery and associated power distribution system to provide sufficient high electric current at short intervals to crank the internal combustion engine in order that it may start. The distribution system must also provide current to the coil in order to achieve engine ignition.
Another important function which must also be provided is that of reserve current to provide lighting and ignition for the vehicle if the vehicle's generator is not operating.
The electrical current requirements of the starter motor are vastly different form those of the vehicle's auxiliaries, such as lighting and ignition. On the one hand, cranking requires large amounts of current for a relatively short duration as the starter motor cranks the internal combustion engine against the compression of the cylinders. Ignition and other vehicle auxiliaries, however, require lower current rates but for long periods of time.
The conventional SLI battery and associated distribution system is therefore designed first to provide sufficient cranking power, and secondly to provide current to the vehicle's auxiliaries whilst the generator is not working. One other function is to act as a voltage load leveller as part of the vehicle's electrical circuits whilst the generator is operating.
It can be said that the conventional SLI battery is primarily a starting battery. However, as the automobile has become more electrically sophisticated, the need to cater to increased auxiliary power demands has placed extra demands on the SLI battery, resulting in the possibility of frequent accidental discharge through the auxiliary circuits.
Engine starting requires larger electrode plate surface areas to provide sufficient cranking capacity. SLI batteries contain cell structures having multiples of thin plates as opposed to thicker plates in order to provide sufficient high current discharge for cranking.
Space restrictions within a vehicle prohibit larger or thicker plates. Thinner electrode plates, whilst suitable for rapid discharge and recharge, are not compatible with longer, slower and deeper discharge cycles which result from auxiliary power use.
When thin plates are subjected to deep discharge as could happen by accidental discharge through auxiliary circuits they tend to buckle, or lose some active material. Positive plates used in conventional SLI constructions also utilize a paste mixture of active material which increases the ability of the plate to dump current (rapid discharge) but also limits the plate's abilities to recover from the effects of deep discharge.
Attempts to overcome these problems have been made by a number of people. Thus, U.S. Pat. No. 406,822 in the name of Dey shows a battery which is divided into two cell groups by an internal dividing plate. U.S. Pat. No. 1,924,959 in the name of Patterson shows four cells, two of which are in series and two of which can be configured either in parallel or series by the throwing of a switch. The cells are totally separate. U.S. Pat. No. 3,029,301 in the name of Strider shows a construction in which two battery parts are provided in series so that six and twelve volt voltage sources can be provided. U.S. Pat. No. 3,242,009 in the name of Schilke shows the construction in which two battery parts are provided, but these are used to provide a number of different voltages. U.S. Pat. No. 3,475,221 in the name of Jordan shows two separate batteries in one container.
U.S. Pat. No. 3,758,345 in the name of Toth shows a construction in which a small auxiliary battery is provided in a shaped recess formed in the main plate. U.S. Pat. No. 3,883,368 in the name of Kordesch shows a construction in which two or more current rates are provided by the use of different types of electrodes, and U.S. Pat. No. 4,684,580 in the name of Cramer shows a construction wherein the casing for the battery has a pocket or recess into which a second or auxiliary battery can be provided.
None of these patents show a construction wherein the problems of the large but short duration current required for cranking and the lower but longer duration demand required by the auxiliaries is able to be coped with in a single battery system configuration. U.S. Pat. No. 3,883,368 does disclose a battery which is able to cope with differing current rates, but this is only achieved by the use of different electrodes, and is not suitable for SLI applications. U.S. Pat. No. No. 4,684,580 in the name of Cramer could provide a construction in which different current draw offs are provided, but this is achieved only by the use of two quite separate and distinct batteries, one of which is able to be mounted on the other. Such double battery constructions require extensive changes to be made to the vehicle electrical architecture and are expensive to manufacture.
Some battery systems have been designed to overcome inconvenience to the vehicle user caused by accidental battery discharge. These include the placement of dual or multiple batteries in vehicles, thereby increasing available capacity. Double battery systems have also been developed. These double battery systems are based on the two-batteries-in-one concept whereby a main battery and a reserve battery are contained within a single structure, and a heavy switch and blocking diode system are incorporated between the main and the backup reserve battery. The blocking diode is used to prevent discharge of the backup reserve battery, while simultaneously providing charge current to that backup reserve battery. These batteries also require a switch between the two batteries, which switch must be capable of carrying the load required to crank the vehicle. Accordingly, the switch is heavy and requires manual operation to place the two batteries into electrical parallel. Such switch backup battery constructions are expensive to produce because of the heavy current diode and switching required. In recent times, batteries have been increasing in size to overcome the problem of accidental discharge. High cold cranking amp batteries using a large number of thin multiple electrode plates are being installed into vehicles to counter the effects of increasing auxiliary electrical power load requirements.
As electrode plates become thinner, the number of plates per cell can be increased. However, this does not adequately solve the problem and does in fact result in plates being too thin to withstand the pressures of deep discharge that become more and more common as the demands on auxiliary power in the car increase.
From the above, it can be appreciated that prior efforts have simply been unsuccessful in providing a practical power distribution system for use in automobile applications, for example, that satisfies the different cranking current and auxiliary current demands and which avoids loss of cranking current due to accidental battery discharge. A power sound and related electrical system for overcoming these problems has not been previously available.
It is therefore an object of the present invention to provide a power distribution system which will at least obviate or minimize the foregoing disadvantages.
Accordingly, the present invention overcomes the problem of the differing current demands placed on the same battery by the modern automobile. The present invention includes an electrical power distribution scheme which allows for discharge and recharge management of cells within the battery structure without requiring heavy duty switches or major electrical alterations to the electrical architecture. While it is possible to overcome the problem of variation in current requirements within an automobile by installation of two or more batteries, the cost to the consumer is a disadvantage, and space constraints in many automobiles make this impractical.
Accordingly, it is an objective of the present invention to provide a cost effective alternative for the consumer.